In U.S. Pat. No. 5,640,926 of the present inventor issued Jun. 24, 1997 is disclosed a feeder for animals, primarily pigs, which includes a shelf on to which feed is deposited from a hopper, the shelf being located above a trough into which feed can fall from the shelf. In this feeder, the height of the shelf from the trough is adjustable so as to accommodate a change in size of the animals from a smaller size up to a larger size as the animals grow.
In U.S. Pat. No. 2,543,916 of Lewis issued Mar. 6, 1951 there is shown a feeder for poultry which has a hopper discharging directly into a trough. The trough is designed so that its width can be increased. In addition the trough has vertical side walls each of which carries a tubular member at its upper edge and defining a top of the respective side wall. The height of the tubular member can be adjusted by releasing a pair of wing-nuts and sliding the tubular member vertically to an adjusted position. The top edge of the tubular member thus defines the height of the side wall. A bottom surface of the tubular member overhangs the base of the trough. It is believed, although not clearly stated, that the height adjustment of the side walls is provided in order to accommodate vertical movement of the side walls of the hopper so that more or less feed can be provided within the trough. Thus as the side wall of the hopper are moved vertically upwardly to provide more feed in the trough, so the side walls of the trough are raised to accommodate that increased amount of feed. This arrangement may be suitable for poultry but is unsatisfactory for animals such as pigs in that the shape of the side walls will interfere with the animals extracting the feed from the trough thus causing some stale feed to be left underneath the side walls.